Fueling tanker trucks are typically constructed as an elongated, horizontal tank having a number of internally divided compartments with various unequal volume capacities to store and transport gasoline, fuel oil, aircraft fuels, or other volatile liquids and fuels. Gasoline tankers are typically bottom loaded through load only or load/unload couplers located below the tanker undercarriage. Vapor rails, channels, or trunks extending along the outside top of the tank include pressure valves tending to generally equalize the vapor pressure at the top of each compartment.
Normally one or more tanker compartments are provided with a large manhole or hatch at the top of the tank. The manhole is covered by a hinged hatch cover which must be sealed liquid tight when closed. Gaskets and other devices are provided for this purpose. One or more of the hatch covers or the upper tank wall itself mounts a vapor pressure relief valve or vent valve operable to allow the escape of vapors from the top of a tank compartment to the atmosphere when excessive pressure builds above a predetermined pressure, such as, for example, 1.0 psi or, any other pressure design parameter. The vent valve also enables the intake of air to relieve predetermined excessive vacuum or negative pressure at the tank top, such as, for example, minus 6 ounces psi. These positive and negative pressure conditions normally appear during loading, unloading, a rise in tank temperature or a decline in tank temperature.
There is a need for a simple unitary relief valve mechanism that efficiently relieves excessive pressure or vacuum in a transportation tank or the like. There are many stringent requirements for such a valve. It must contain a number of fail-safe features. In the event of tank roll-over at any angle, for example, the valve must prevent excessive loss of lading. On either excessive pressure or vacuum, the action of the valve must be quick and positive.
Current valves are tested in static conditions. However, it is known that during transport, a transportation tank is subjected to vibrations as the truck travels over rough road conditions such as bumps or potholes. When the transportation tank does vibrate, it is common for the valve to release vapors below the static pressure of the valve.
Notwithstanding the state of the art as described herein, there is a need for further improvements in tank pressure and vacuum relief valves for fuel tanker trucks that can withstand tank vibrations so as to prevent the release of vapors below the static pressure of the valves.